[derefr]

> the authorities will call the number you put on that card to see if you're there or if you've checked into the hotel

So... what happens when you’re not there? I.e. if the government just can’t find you? Does this then translate to a police APB or something?

[frankacter]

"My phone, which is satellite-tracked by the Taiwan gov to enforce quarantine, ran out of battery at 7:30 AM. By 8:15, four different units called me. By 8:20, the police were knocking at my door."

https://twitter.com/MiloHsieh/status/1241540231595044864?s=1...

[derefr]

I meant in the case of a visitor to the country who hasn’t purchased a local SIM yet, where the only contact information on the customs form is the hotel’s front-desk number.

[hailwren]

They'd follow you from the airport. You could maybe evade if you were a trained expert who looked like a local national, but otherwise they'd just check CCTV (Taipei is covered in it) and follow your trail. I've never taken public trans out of TPE, so they'd probably just call the cab company and track you down that way. Otherwise, they would check the public trans cameras.

Also lack of local sim doesn't mean you aren't transmitting. It just means the towers are choosing not to provide you with service. A SIM's only purpose is to link your usage to a billing account and phone number.

[derefr]

> Also lack of local sim doesn't mean you aren't transmitting.

Yes and no. Airplane mode, turning your phone off, etc.

But also, even if your phone is pinging the tower with your device’s IMEI... how would they know it’s your phone’s IMEI? There’s no registry mapping IMEIs to legal identities, in any country, AFAIK. Carriers have that information, but you wouldn’t have yet signed up with any Taiwanese carrier. So the Taiwanese government could only get that information from a foreign carrier.

(Yes, you could plug all the tower pings into a graph DB and run Dynamic Network Analysis to figure out what common unidentified IMEI matches the route pattern you extracted from the CCTV data—but you’re expecting a lot here; that hardly works even when you have tens of thousands of bits of evidence of e.g. a crime ring; and that kind of analysis is one of the “slow checks”, like DNA PCR assaying, that takes months to run—especially if you’re having to go process-of-elimination by adding everyone else’s IMEIs into the graph to find the “UFO” IMEI [which presumes that doesn’t also involve O(N) warrants somehow. I’ll be nice and assume it doesn’t.] Add the fact that the only people trained in Network Analysis will be in your country’s fraud squad, and someone between Customs Enforcement and Fraud will have to come up with the idea of getting the fraud people to use this technique outside of its usual domain of application, and... not seeing it happening.)

Basically, for the Taiwanese government to know your phone’s IMEI, you would have either had to tell them the IMEI on the customs form†; or they would have to ask your previous phone provider in your country of origin what IMEI they last saw registered to your IMSI (in turn attached to the phone number on your customs form); and then, provided your domestic provider had any reason at all to want to answer that question (they certainly wouldn’t be compelled to), then the Taiwanese govt would be able to track you.

But that helps nothing if, again, you just provided the phone number of the hotel you’re staying at as your “contact number” on the customs form, as they ask you to. Then they’d need to take another step back and figure out what your cellular numbers in regular use are, given only your other details, without even knowing what carriers you have relationships with in other countries. (Sure, okay, look it up on LinkedIn. That works for a normal person. I’m assuming a person motivated to hide here.)

It also helps nothing if you bought a new phone at any point between when you last signed up for a SIM in your last country of known residence, and when you showed up in Taiwan; and it also helps nothing if you just set your phone to spoof your IMEI. (IMEIs are like MAC addresses: a hardware-fused default with a software-programmable override!)

† ...or they could read it off the millimeter-wave scan of your phone they took at the airport, if they tune the scanner just so. That solves everything for them except the IMEI spoofing, really.

[hailwren]

They wouldn't use the IMEI. Your phone also reports the IMSI which includes country code, network, and an identifier number. They'd only have to differentiate you from the other people from your country. By the problem statement, you didn't go straight to your hotel -- so you're probably going to be the only one.

And sure, you could leave it on airplane mode -- but you have to keep in mind that you are eventually going to be found, and I'm not really clear why we're even evading quarantine but when you are found the punishment is going to be much more severe if the government believes that you were intentionally avoiding detection. Keep in mind, Taiwan still punishes drug trafficking with death -- I can't imagine they'd look kindly on intentionally endangering their entire population.

Although upon further thought, IMEI should be fine too. Consider that international travel is mostly shut down right now. I'd be surprised if there are more than 500 international travelers at the airport within 30 minutes of you. They would just check every one against their quarantine reporting status (hint: EVERYONE else will be where they're supposed to be and checking in as part of the procedure) Then all you have to do is remove IMEIs that are at their correct reporting location one by one. I'd guess less than a hour's work given that the reporting is already being handled.

[barkingcat]

This is probably thinking too high tech for some basic human int collection. It's easy enough to collect imei numbers at a checkpoint. It's also easy enough to find out from family members and friends and business connections (everyone works for someone, has a family, and friends, and even if none, there's always a bank account that paid for the airline ticket somewhere, attached to a passport).

Think low tech. Taiwan didn't even have a computerized registry when I was born, so everything was done by hand (I can confirm this because when I had to look up my birth certificate, it wasn't in the records! and they had to look up the records by hand - but the records exist and are easily findable by humans)

also, don't neglect a simple phone call from the police to your boss - that's a super easy way to find out what's going on. Especially for Western folks who seem to be tied to their work.

[derefr]

> It's easy enough to collect imei numbers at a checkpoint.

True enough, I guess. Require that you turn all devices on, then either require unlock and look at the IMEIs yourself, or pass the person through a Stingray in an RFID cage.

But I would assume that if Taiwan was doing that, people would notice (requiring turning devices on is a very unusual step) and would have mentioned online somewhere that that’s something that happens when you visit Taiwan.

Also, it still won’t help if this immigration-evader turned super-spy is rolling their spoofed IMEI regularly.

(Also, where would they get the information on who your boss/company is? From your customs form? That’s one of those things too expensive to verify for every case ahead of time, so they won’t bother until they actually want to find you; in other words, that’s one of those things that’s perfectly easy to lie about. From your visa, presuming you need one? Information like that could be entirely outdated by the time you visit.)

[frankacter]

If you don't have a device/sim, one is provided.